The injector is a part which comprises one or more injection elements allowing the combustion unit to be fed with the propellant(s) necessary for its operation, such that there is rapid and complete mixing of these propellants so as to ensure stable and homogeneous combustion.
In the case of engines using cryogenic propellants, it is customary to employ injectors using injection elements with coaxial jets. However, such an injection system is not suited to all operating conditions, and in particular, it rapidly exceeds its limits and gives unsatisfactory results when high performance is demanded as regards the injection of very high propellant flowrates. With such a system, it is therefore not possible to expect significant cost savings.
By contrast, the injector geometry described in the NASA report "Noncircular orifices holes and advanced fabrication techniques for liquid rocket injectors", published in the journal: NASA CR 134315 MAY 1974, allows operation at high flowrates to be envisaged, the different injection elements having a structure with rectangular slits, the performance and characteristics of which are independent of the injected flowrate. Nevertheless, the geometry is not entirely satisfactory because it is not simple to produce, the integration of the elements into an injector being particularly complex, and moreover, the performance which results is greatly reduced by incomplete mixing at the ends of that slit due to the presence at that location of an excess of hydrogen relative to oxygen.
Patent U.S. Pat. No. 3,446,024 seeks to suppress this end effect by producing an injector with an injection element which is circular rather than rectilinear. However, the geometry disclosed in that document restricts possibilities of arranging a plurality of injection elements at a single injector, and the way in which propellants are fed to the different sheets does not guarantee identical flowrates for the propellants, i.e. quality flows and therefore good combustion.